Project 3 Abstract Immunotherapy has emerged as an exciting new strategy in cancer treatment. The development of antibodies that can block negative immune regulatory pathways have resulted in clinical improvements in cancer patients that was not seen previously. Because of this success, there has been strong research and clinical interest in developing strategies to further improve cancer immunotherapy. One key strategy has been to utilize radiotherapy to enhance immunotherapy effects. Radiotherapy is thought to increase the antigen exposure to the immune system. There is also growing preclinical data demonstrating that nanoparticles (NPs) can enhance immunotherapy by improving antigen presentation. We hypothesize that we can engineer NPs that can capture the antigens released by radiotherapy and such NPs can enhance the effects of immunotherapy. We have preliminary data demonstrating that NPs can indeed capture tumor antigens released from radiotherapy. We have termed these NPs antigen-capturing NPs or AC- NP. Using a mouse model of melanoma, we have demonstrated AC-NPs, when given in conjunction with ?CTLA-4 antibody, can improve immunotherapy efficacy. The therapeutic efficacy of AC-NPs are dependent on the NPs' surface properties. We have also demonstrated that AC-NPs, when injected into tumors after radiotherapy, can generate systemic immune response against tumor cells in mice. The central goal of this application is to develop NPs that can effectively capture tumor antigens released by radiotherapy and evaluate these NPs in cancer immunotherapy. Our application has 3 specific aims: Aim 1: To optimize the size and surface chemistry of AC-NPs for capturing tumor antigen released from radiotherapy Aim 2: To determine whether AC-NPs can enhance the abscopal effect by radiotherapy. Aim 3: To determine whether AC-NPs' efficacy in enhancing the radiation therapy abscopal effect can be further improved by the addition of tumor microenvironment modifiers. To accomplish this goal, we plan to engineer biocompatible and biodegradable NPs with various size and surface properties. Melanoma will be used as a model disease for our work since it is a disease that has clearly benefited from immunotherapy. Furthermore, there are well-established mouse melanoma models for immunotherapy and extensive research using these tumor models. Our application combines concepts from several disciplines: nanotechnology, immune therapy and radiotherapy, in developing a novel strategy to improve cancer immunotherapy. Our work can increase the response rates of cancer immunotherapy which will directly translate into increased cure and survival in patients. While our work is focused on melanoma as a model, our results may be broadly applied to other cancers.